Black 13 has a similar, but smaller, effect to that of White 12. It
could be replaced by an extension to B but 13 by White will then
threaten strong invasion.

Black 15 is necessary to prevent white from jumping any nearer the
black group after the attack with 14.

White 16 is to discourage black from invading at C and threatens to
wall black in at 17, leaving Black with a small live group and no
influence at all in this area.

White 18 still threatens to enclose black.

White 20 is good form, better than any other move in this area.
Also white cannot cut black at 21 because of Dia 1,
attacking the white group.

Black 21 concludes the sequence stared with 18 by which White has
strengthened his lower group with sente. White now has time to support his
last corner with 22 giving Black a choice between extension along the
top or down the right hand side.

Black 23 stops White forming an ideal formation of 5 stones in the
top left corner.

White 24 then automatically grabs the other side - 24 is the best
point - and now threatens to dominate the lower centre and right part of
the board. Should black invade the corner white would wall him in and
feel very pleased with his great outward influence from his right and
left groups working together.

Black 25: So Black plays the usual attack and pushes further into
the corner to strengthen his group against attack.

White 32 is not the best way for to do something about Black's
great sphere of influence and good prospects in the top right corner; H
is better, and if black replies at 32 then white invades at, for
example, 34.

Black 33 is a good defensive move, though heavy, because it
anticipates 39.

White 34: Light, as it should be. Heavy play is far worse when
attacking than when defending.

White 38 is best. If White is tempted to play 42, black will just
cut at 38.

Black 39: The profitable move, threatening invasion of the corner,
for example at J, which White should have anticipated at move 32.

White 46 protects against a black invasion of White's territory,
which black's creep to the left is threatening despite the strengthening
exchange of 40 for 41. Now Black takes as much profit as he can in this
bit of the board and then turns elsewhere ...

Black 59: An excellent move, increasing Black's territory while
preventing White from doing likewise with the same move.

White 60: After 59, this is the furthest that white can safely come
into the black group.

White 64 is the usual attack on this corner formation and 65 the
usual defensive reply on that side.

White 66, 68: help to make White's large group alive.

Black 69 threatens K or L spoiling White's territory. But it is a
risky move because it can be cut, as happens with the game, thereby
jeopardising Black's chances in a position that is favourable to him,
thanks to White's earlier mistake (32).

Black 75' could be changed to N as in Dia 2.
This either captures three white stones or connects to the black stones
above.

White 80 is the best way to save the two stones and prevent black
from invading. Black now tries to connect to the top right corner but
fails and has to try and make eyes in the centre or connect to another
black group.

Black 93: Black supposed that this gave him the chance of playing
at L later, but this is answered by M.